Communication devices such as User Equipments (UE) are also known as e.g. mobile terminals, wireless terminals and/or mobile stations. User equipments are enabled to communicate wirelessly in a wireless communications system or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two user equipments, between a user equipment and a regular telephone and/or between a user equipment and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications system.
User equipments may further be referred to as mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some further examples. The user equipments in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as user equipment or a server.
The wireless communications system covers a geographical area which is divided into cell areas, wherein each cell area being served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the user equipments within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for user equipments. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
According to 3GPP GSM EDGE Radio Access Network (GERAN), a user equipment has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction. EDGE is an abbreviation for Enhanced Data rates for GSM Evolution. In the end of 2008 the first release, Release 8, of the 3GPP Long Term Evolution (LTE) standard was finalized and later releases have also been finalized.
In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In network assisted Device-to-Device (D2D) communications, a network such as a radio access network assists user equipments that are in the proximity of each other to discover one another, referred to as device discovery, and establish a direct link referred to as D2D bearer establishment, rather than a link via the base station 110. In fact, when two user equipments communicate with each other via a cellular base station, the communication path involves an uplink and a downlink, both with associated resources, as opposed to the single hop direct D2D link.
Network assisted D2D communication refers to two distinct cases in terms of the number of base stations or wireless access points, such as eNB, that are involved. In a single eNB case, both user equipments are connected or camp on, i.e. are served by the same eNB. In a multiple eNB case, the two devices that are candidates for direct D2D communications are served by different eNBs.
In network assisted device discovery the radio access network may, for example, allocate resources for beacon signals, so that transmitting and receiving user equipments know what time and frequency resources being used for device discovery, that is when and at what frequencies beacons should be transmitted and scanned for or received. Alternatively, a user equipment may register at the network for D2D communications. Subsequently, another user equipment may inquire the network for possible peers allowing the network to mediate between, basically to match, the user equipments in finding each other.
The initiation of the establishment of the D2D link may be made by the radio access network or by any of the user equipments of the D2D pair. In network initiated D2D link establishment, the network realizes that two communicating user equipments are in the proximity of each other. In user equipment initiated D2D link establishment, the user equipments discover the proximity of each other and also some of their capabilities which is necessary for them to establish a D2D link, similar to Bluetooth. In both cases, since communication takes place in operator licensed spectrum, current methods allow the eNB, or other network node in the RAN, to control the actually used resources by the D2D link.
In network assisted D2D bearer establishment the network indicates to the devices which time and frequency resources and what transmit power levels they should use for the direct communication. The network may subsequently send periodic commands to the D2D pair regarding the resources that they should use for the direct D2D link. That way, the devices of the D2D pair maintain a cellular control plane, while the user plane is established directly between the devices.
In network assisted D2D communication scenarios, D2D capable user equipments requires to be able to maintain simultaneous D2D and cellular links. These parallel links may be used for the exchange of user plane as well as control plane information. The user equipments that may be candidates for D2D communications may have very different capabilities, ranging from small devices with limited Input/Output (I/O) capabilities to smart phones, tablets and laptops.
In network assisted D2D, prior art techniques allow user equipments in D2D mode to receive paging and control messages from the cellular network. Also, some application on a user equipment may want to establish a cellular connection with its current serving eNB in order to communicate with the core network, while maintaining the D2D link, i.e. simultaneous cellular and D2D communication capability.
If the user equipment needs most of its power resources for maintaining the D2D link, it may not have sufficient resources to schedule uplink cellular traffic to the eNB. Similarly, if the user equipment needs most of its processing power to manage its ongoing cellular links, it may not have sufficient remaining processing power to maintain a D2D link. Therefore, because D2D capable user equipments may open multiple communication sessions at the same time, the quality of the simultaneous sessions may suffer due to the inherent available resources.